When it comes to gloomy weather, dark English interiors and brooding loner detectives “Masterpiece Mystery!” on PBS has it covered. So far this season “Masterpiece Mystery!” has offered up Agatha Christie whodunits: three new episodes featuring the Belgian detective Hercule Poirot and on Sunday a new adventure for the gentle knitter Miss Marple. In September the show heads back to another traditional setting, Oxford University, with new episodes of “Inspector Lewis.”

Before then, however, the producers decided viewers needed a modern Roman holiday. Beginning next Sunday the series takes a very different turn, with adaptations of three books by the British writer Michael Dibdin, centered on his Italian police detective Aurelio Zen.

The soundtrack veers from opera to 1960s-era secret-agent themes. The camera tracks car chases through a lighted-up nighttime Rome and lingers on the Italian countryside. At the center of it all is the actor Rufus Sewell (“Middlemarch,” “The Pillars of the Earth”), more of a heartthrob than the standard “Mystery!” sleuth, sharp suits replacing his usual period dress.

While the Zen mysteries follow the formula of crimes that can be solved in 90 minutes, the series’s broader theme is a departure for “Masterpiece” as well, as Zen tries to maneuver his way around corruption in his own department and the government, with conflicting pressure from all sides in the cases at hand.

“I rather liked that he’s set up to fail,” said Andy Harries, the chief executive of Left Bank Pictures, which — fresh from adapting Henning Mankell’s “Wallander” mysteries, also shown on “Masterpiece Mystery!” — developed the series for the BBC and “Masterpiece.” “The levels of corruption are so immense, so culturally ingrained in Italy,” he said, referring to the scandals involving the Italian prime minister, Silvio Berlusconi. “We might regard it as corruption, but the Italians don’t. It’s just a very, very different culture.”

The tension “makes for quite a subtle show, with the ambivalence and complexities,” he added. “It was designed to push the boat out further, make the viewer work a little harder.”

With “Wallander” and now “Zen,” said Rebecca Eaton, the executive producer of “Masterpiece,” “the way scripts are being written is reflecting a more serious view of life and crime, rather than just a lighthearted escape.”

In a late addition to the “Masterpiece Mystery!” schedule Ms. Eaton also just finalized a deal to add a new detective to the lineup for three weeks starting Oct. 16. “Case Histories,” based on the book by Kate Atkinson, will feature a modern detective named Jackson Brodie, played by Jason Isaacs (who will also appear on NBC in the midseason paranormal series “Awake”). As in “Zen,” Ms. Eaton said, the character is a younger man “with sex appeal,” and the setting, Edinburgh, “provides tremendous geographic flavor.”

Publicity materials for “Zen” paint the character as an “honest cop” bringing “justice to modern-day Italy, whether the authorities want it or not.” Mr. Sewell sees it differently. “Always be very much wary of DVD liner notes,” he said in a telephone interview. While not corrupt in the same sense that his colleagues are, he said, Zen “can be quite morally dubious when it suits him.”

He added: “He has a slightly lackadaisical moral code, a sense of wanting to do something good. But he’s not above kicking someone when they’re down. He’s a gray area, and that’s what makes it incredibly fun.”

Just shy of 40, Zen is separated from his wife and living with his mother. “There’s a certain lack of dynamism in the character,” Mr. Sewell said. “He’s pushed around by tides and circumstances.” (But just as he always solves his case despite the conflicting pressures, he also ends up with the most sought-after woman in the office, played by an Italian actress, Caterina Murino.)

The casting proved a challenge for the producers. With “Wallander,” Mr. Harries explained, it was easy to find British actors who shared the Scandinavians’ pallor; trying to find ones who could play Italians was much harder. Mr. Harries said he had Mr. Sewell in mind for the role from the beginning, because “he has a good Eastern European Mediterranean look about him.”

But while the men are almost all English speakers, Italians were largely cast for the female roles, for creative reasons and also because the project had partial Italian financing. “English girls on the whole simply just don’t have the sensuality and looks of the Italian girls,” Mr. Harries said, quickly adding that “they have different charms.”

The result was a mix of accents, something that “the audience was going to buy or not buy,” Mr. Sewell said. “It takes perhaps a little adjustment.”

The audience for “Masterpiece” soared in the past season, to an average of 3.5 million viewers, up 66 percent from the 2009-10 season, thanks to “Downton Abbey” and an “Upstairs, Downstairs” sequel. And for the first time since ExxonMobil ended its support in 2004, the financing prospects have brightened, as well.

A corporate sponsor, the mutual fund company Franklin Templeton, signed on to support the show from May through September. And a trust established in January to attract individual donors is closing in on its goal of $1 million six months ahead of schedule. For $25,000 each, supporters get their names in the credits, if they wish. “It seems to have hit a sweet spot,” said Ms. Eaton, adding that the donors clearly have an emotional attachment to the program.

Viewers who get too attached to “Zen” may be disappointed, however. While Ms. Eaton said she would love more episodes, Mr. Harries said that because of a change in management at the BBC, “Zen” hasn’t been renewed.

Mr. Sewell said he was philosophical about the situation. “There were rumblings in the air that certain people weren’t that fond of the tone and, for me, I think the tone is it.” He said he’d rather go on to other projects “than try to tinker with it.” But Mr. Harries said he hadn’t given up hope that the character could be resurrected. “I’m still working on it,” he said.